The present invention relates to and has essentially for its object an electromagnetic tripping device, forming for example a relay, circuit breaker or like current interrupting means, designed to meet more particularly two categories of new requirements, i.e., on the one hand, miniaturization of such devices, and on the other hand, the suitability of such miniaturized devices for their most currently contemplated use, namely, their mounting on printed-circuit cards as any other electronic components.
Accidents with catastrophic consequences have recently occured in certain data processing centers and telephone exchanges using important digital processing installations. In such cases, whole cabinets full of printed-circuit cards plugged side by side into connectors arranged in rows are enclosed in a same room. The printed-circuit cards are usually arranged vertically in order to facilitate ventilation and the spacing between the cards in a same row is practically standardized to correspond to the maximum width of the largest electronic components used. A complete installation of this kind using several cabinets full of electronic components is obviously very expensive. On the other hand, the risks of failure of the installation are not inconsiderable in view of the number of components. It has happened that a fault in just one printed-circuit card resulting in a short circuit has started a fire which has destroyed the whole installation. Designers have therefore recognized the necessity for equipping each printed-circuit card with one or several individual circuit breakers designed to immediately cut out at least part of the card on occurence of an abnormal current at the card, e.g. in the direct-current supply. The needed next type of circuit breaker was therefore a miniature circuit breaker with the following mutually conflicting characteristics:
it had to be miniaturized in the extreme in order to be of a size compatible with the mean size of the electronic components mounted on the printed-circuit cards of present-day digital processing systems,
in particular, it must have a minimum base area in order not to be too difficult to be mounted on the printed-circuit card, and its height must be greater than the usually adopted spacing between the cards arranged vertically within a common cabinet,
its sensitivity must be increased so as to be compatible with the usual orders of magnitude of the supply currents for such printed-circuit cards,
lastly and above all, the tripping knob must be arranged on the side of the circuit-breaker housing so that when the housing is adequately mounted on the card the said knob is readily accessible and does not prevent other components being mounted in immediate proximity to the circuit breaker.
Devices meeting such requirements in association with those of miniaturization proper (reduced number of members, accurate assembly, etc.) are practically unavailable on the market. The present invention is the result of extensive research with a view to making all such requirements compatible with one another. Otherwise stated, the shape and arrangement of the components of the device according to the invention as well as its external appearance have been conceived essentially for its contemplated application. However, the same basic structure may be quite easily reutilized to develop an electromagnetic relay with quite as interesting performances.